Lab Report Pka of Methyl Red

Determination of the pKa of Methyl Red
by UV-Vis Spectroscopy

February 16, 2010
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ABSTRACT
The purpose of this experiment was to withstand the pKa for an loony toons-base indicator. A spectrometer was used to take care the pKa of methyl carmine. The standardization curves were created by analyzing samples of known concentration at pHs well above and below the pH indicator roll for methyl red. Then samples of known pH were analyzed. By, solving the formation of comparabilitys using linear algebra, the concentrations of the indicator and the conjugate base were determined. The Henderson-Hasselbach equation predicted that the pH for these solution plotted against the pound of the ratio of the twain species would yield a line whose Y-intercept equaled the pKa for methyl red. The value obtained was 4.96(1), which has a percent error of 1.9. Perhaps, if this were corrected for temperature there would be blush greater agreement with the accepted value.

INTRODUCTION
The purpose of this experiment was to determine the pKa of an acid-base indicator (methyl red). All indicators are weak acids, and as such(prenominal) have a dissociation constant, or Ka. The subscript a signifies that the constant is for an acid. The lower case p indicates that the value is the detrimental log (base 10) of the constant.



The Ka expression,
Ka=H+In-HIn[1] (1)
is the equilibrium for the dissociation of the weak acid, where HIn is the acid and In- is the conjugate base. This is represented by the chemical equation:
HIn ?H++ In-
[1]Figure 1: Chemical equation for the dissociation of an acid-base indicator.

Methyl red is a monoprotic organic acid. Figure 2 is a structural model of methyl red.

Figure 2: Chemical twist of methyl red
By plotting the data as the pH versus the log term of the Henderson-Hasselbach Equation,
pH=pKa+logIn-HIn[2](2)
the pKa was determined. The plot was linear with the Y-intercept equaling the value for the pKa. The pH was determined...If you want to get a full essay, order it on our website: Orderessay



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